1. Field of the Invention
The present invention relates to a method of laser cutting a metal line on a magneto-resistive (MR) head and more particularly to a method of laser cutting a metal line which shorts leads to an MR sensor in the MR head.
2. Description of the Related Art
MR sensors are commonly used as read elements in thin film magnetic heads for sensing recorded signals on a magnetic medium, such as a magnetic disk. A thin film magnetic head, which incorporates an MR sensor, is called an MR head. An MR sensor includes a thin stripe of conductive material, such as Permalloy (NiFe). When a magnetic medium, such as a magnetic disk, is rotated adjacent the stripe, magnetic fields from the medium cause the stripe to change its resistance. A sense current conducted through the MR stripe changes its magnitude proportionally to the change in resistance. The magnitude changes are then processed by channel electronics into playback signals representing information stored on the magnetic medium.
A typical MR stripe is 3 .mu.m wide, 2 .mu.m high and 200 .ANG. thick. The length and thickness of the MR stripe are exposed at an exterior surface of the MR head while the height is buried in the head body. During construction and assembly of the MR head, the MR stripe must be protected from electrostatic discharge (ESD). A discharge of only a few volts can destroy or severely damage the MR stripe. Such a discharge can occur by contact with or close proximity to a person, plastic involved in the fabrication, or components of a magnetic medium drive.
The MR sensor is positioned between a pair of thin film gap layers which are in turn sandwiched between a pair of thin film shield layers. A pair of thin film leads, which are employed for transmitting the sense current through the MR sensor, also lie between the gap layers. The leads terminate at a pair of pads which are exposed for connection to drive electronics. A convenient way of protecting the MR sensor from ESD is to interconnect the pads with a thin film conductive line on the exterior surface of the MR head. This shorts the MR circuit, preventing discharge across it. The best time during assembly of a magnetic disk drive to form the conductive line between the pads is at the row level which will be explained hereinafter.
Magnetic heads are typically formed in rows and columns on a wafer of titanium carbide (TiC). After formation of the magnetic heads, the wafer is cut into rows. At the row level the thin film conductive lines are formed between the pads for shorting the MR sensors. Each row is then cut into individual heads with a portion of the TiC wafer serving as a slider for supporting a magnetic head. Each slider with a head mounted thereon is mounted on a head gimbal assembly (HGA), which is in turn mounted on a suspension, which is in turn mounted on an actuator arm. A plurality of actuator arms may be mounted in an actuator assembly to form a head stack assembly. From the time of forming the conductive lines up to the time of forming the head stack assembly the MR sensors have been protected from ESD. The next step is to merge the head stack assembly with a disk stack assembly to form a completed disk drives which step is simply referred to in the art as "merge". The most practical time to sever the conductive line of each MR head so that the MR sensor becomes operational is just before merge.
Heretofore, the conductive lines have been severed by chemical etching or physical sputtering. Both of these methods are cumbersome after the head stack assembly has been formed and both methods impact the entire head. When sputtering is employed it is very difficult to avoid damaging the head and to prevent debris from forming. Debris from the head can be especially troublesome because of the potential of containing the disk drive. Consequently there is a strong felt need to provide a simpler method of severing the conductive line in the MR sensor circuit without generating debris.